Electric circuit breaker with magnetic tripping means



Jan. 7, 1969' J. F. JOHNSON T ELECTRIC CIRCUIT BREAKER WITHMAGNETICTRIPPIN MEANS Filed June 19, 1967 3 WW 1 i j aw 5 MM 6 4 e000 F m aMw VR 5 mwwcm -wwfi w T WFZ A mu 3 United States Patent 5 Claims Int. Cl.H01h 75/12; H01h 77/04; H01h 81/00 ABSTRACT OF THE DISCLOSURE Alatch-trip type electric circuit breaker, including a thermal-magneticcurrent responsive tripping device; the tripping device includes agenerally channel-shaped field piece, a confronting generallychannel-shaped armature, a cylindrical core member carried by the fieldpiece between the two members, and an energizing coil surrounding thecore; a bimetallic strip extends between the end of the core member andarmature and is so located with respect to the air gaps between thefield piece and the armature that although some leakage flux goesthrough the bimetallic member, all the flux, including such leakageflux, goes across the working air gaps of the magnetic assembly, wherebyto provide a compact and s nsitive thermal-magnetic tn'p assembly.

Background of the invention Field 0 the invention.The present inventionrelates to latch-trip type electric circuit breakers, and moreparticularly, to electric circuit breakers of the type includingcombined thermal and magnetic current responsive means for causingreleasing of the latch and automatic opening of the circuit breaker uponthe occurrence of predetermined current conditions therethrough.

Description of the prior art.--An electric circuit breaker of thegeneral type referred to is shown in prior Patent 3,162,739, K. W. Kleinet al., issued Dec. 22, 1964 (Class 200-88) and assigned to the sameassignee as the present invention. In circuit breakers of the latch-triptype, thermal means comprising an elongated bimetallic strip is providedfor causing unlatching or tripping of the circuit breaker upon theoccurrence of current conditions above the nominal rating of the circuitbreaker which persist for a predetermined length of time such as tocause sufiicient heating and warping of the bimetallic strip to cause itto engage and actuate a trip member. In addition, magnetic actuatedmeans is provided for causing substantially instantaneous latch releaseupon the occurrence of high excess currents such as short-circuitcurrents if they are in the range of about 6 to 12 times the nominalrating of the circuit breaker.

In circuit breakers of medium and high capacity, the magnetic trippingstructures can be extremely simplified, such, for example, as comprisinga generally U-shaped magnetic field piece and a generally flat platetype armature with a single current carrying conductor passingtherebetween providing, in eifect, a single turn winding. The currentcarrying conductor may be a bimetallic strip, or a conductor acting as aheater for the bimetallic strip, as in the above-mentioned patent. Suchsimplified structure is possible because in these current ranges, theamount of current in the 6 to 12 times range at which the devices arerequired to operate is sufficiently high (400 amperes or more) toprovide substantial force even with such simplified magnetic structures.In lower ampere ratings, however, such, for example, as 15 through 50amperes, more sensitive devices are required, such as devices capable ofoperating as low as 90 amperes. Such sensitive magnetic tripping devicesrequire multi-turni rather than single-turn windings. If the turns onthe windings are of substantial number, a conflict arises with the spacerequirements, since such devices are also required to be extremelycompact.

Summary 0 the invention It is an object of the present invention toprovide an electric circuit breaker of the latch-trip type includingcombined thermal and magnetic tripping means which is both sensitive andextremely compact.

It is a further object of the invention to provide a circuit breaker ofthe type described including a combined thermal-magnetic trip device inwhich the bimetallic strip is directly heated and is also used to form aportion of a turn of the magnetic device winding without detracting fromthe magnetic eificiency of the magnetic trip device.

In accordance with the invention in one form, an electric circuitbreaker of the latch-trip type is provided including a trip member whichis normally held by a trip bar, the trip bar being actuated by trippingmeans located in each of three poles of the circuit breaker. A trippingmechanism in each pole of the circuit breaker includes a stationarymagnetic field piece having a back wall which supports a generallycylindrical core member extending at right angles thereto and carrying amulti-turn energizing winding. A movable armature is included ofgenerally U-shaped cross-section and includes side portions extending oneither side of the coil and core assembly so that current through thecoil sets up magnetic lines of force which emanate from one end of thecylindrical core member, pass through the armature member, and thenceback through the sides of the armature member across the pair of airgaps between the ends of the side wall and the stationary field piece. Abimetallic strip is mounted in cantilever fashion adjacent the magneticassernbly and passes between the armature and field piece. The sidewalls of the armature accordingly extend substantially beyond thebimetallic strip before terminating to form air-gaps with relation tothe field piece. Because of this arrangement, although some leakage fluxpasses transversely through the bimetallic strips, this does not detractfrom the sensitivity of the assembly since all flux including suchleakage fiux goes across the air gaps to cause actuation.

Brief description of the drawings FIGURE 1 is a side elevation view ofan electric circuit breaker incorporating the invention, a portion ofthe side wall of the casing being broken away to show the internal partsand particularly the trip unit assembly;

FIGURE 2 is a side elevation view of the trip unit assembly of thecircuit breaker of FIGURE 1, the side of the enclosing casing of thetrip unit nearest the observer being removed to show the internal parts;

FIGURE 3 is anexploded perspective view of a portion of the trip unitdevice of FIGURE 2;

FIGURE 4 is a sectional view of the parts of the assembly shown inFIGURE 3 but illustrated in assembled relation, and

FIGURES 5 and 6 are illustrations of other alternate possiblearrangements, shown for purposes of discussion.

Description of one embodiment The invention is shown as incorporated inan electric circuit breaker including a generally rectangular insulatingcasing 10. (For purposes of simplification, only a single pole chamberis illustrated. It should be appreciated, however, that the embodimentdisclosed is a three-pole cuircuit breaker and that each pole thereofincludes a current path and current tripping parts similar to those tobe described in connection with the selected pole.) The pole chamberillustrated includes a power incoming terminal 11 supported in theinsulating casing 10 by suitable means,

not shown. The current flows from the incoming power terminal 11 throughseparable contacts (not shown) to the incoming terminal strap 12 of thetrip unit 13, and from the outgoing terminal strap 14 of the trip unit13 to an outgoing or load terminal 15. The circuit breaker contacts (notshown) are operated by suitable operating mechanism (not shown) whichmay be actuated by an actuating handle member 16 projecting from the topwall of the circuit breaker casing 10. The operating mechanism includesa releasable trip member 17 which is normally held from tripping actionby latch means included in the trip unit 13 to be described.

The trip unit 13 includes an insulating casing comprising two generallycup-shaped parts 13A and 133. A rigid conducting strap 18 is mounted onthe insulating base portion 13A by suitable means such as by rivet 19and is connected to the terminal member 12 at one end and supports arigid upstanding bimetallic member 20 at the other end. The upper ormovable end of the bimetallic strip 20 carries a calibrating oractuating screw 21, and has connected thereto a flexible conductormember 22 which extends to and is connected to an energizing coil 23,which in turn is connected to the outgoing terminal 14.

The releasable trip member 17 is normally held by a latch member 25which is pivotally supported at 26 in the insulating casing part 13B.The latch member 25 is biased counterclockwise to the position shown bysuitable biasing means, not shown, and includes a latch projection 25Awhich engages and restrains the tip of the trip member 17. The latchmember 25 also includes a magnetic common trip bar portion 2513 whichpermits actuation of the latch member 25 by the magnetic tripping meansof any of the poles of the breaker in a manner to be described. Athermal common trip bar 27 is also provided and is pivoted on the samepivot axis as the latch member 25. The thermal trip bar 27 extendsacross all the poles of the circuit breaker to permit actuation by anyof the thermal trip members of any of the poles. The thermal trip bar 27includes a projection 27A which engages the latch member 25 to causerotation of the latch member 25 in clockwise direction upon clockwiserotation of the trip bar 27.

For the purpose of causing movement of the latch member 25 in releasingdirection by the magnetic actuating means to be described, a generallyH-shaped intermediate actuating member 28 is provided (see FIGURE 3)which is also pivotally supported on the same pivot pin 26 as the latch25. The actuating member 28 includes a pair of projecting portions 28Awhich overlay portions of the magnetic trip bar 25B. The actuatingmember 28 is biased counterclockwise at all times by the adjustabletension spring member 29. The tension spring member 29 is adapted to beadjusted by rocking movement of an adjusting lever 30 which is retainedin desired position by an adjusting screw 31 threadedly engaged in theinsulating casing part 13A. The actuating member 28 is biased by thespring 29 against a cam member 32 as a stop. The cam members 32 forms apart of a rotatable adjusting assembly which is adapted to be rotated byan externally accessible adjusting knob 33.

The actuating member 28 has attached thereto a generally channel-shapedmagnetic armature member 35, which is adapted to be moved thereby towardand away from a generally channel-shaped stationary magnetic field piece36. (As used in this application, the term magnetic refers to a metallicmaterial having a permeability substantially better than that of air.)The member 36 has its side portions 36A bent up to provide pole portionsto cooperate with the pole portions 35A of the armature 35.

A cylindrical core member 38 of material of high mag netic permeability,is mounted on the field piece 36 by means of the screw 37 which passesthrough the casing wall 13A and through the field piece 36, threadinginto the core member 38. The energizing coil 23 surrounds the coremember 38, as shown in FIGURE 2. The core memher 38 is preferablycovered with a thin insulating covering not shown. Likewise, theconductor forming the coil 23 also is coated with an insulating coating.

Operation 0 the thermal tripping means Upon the occurrence of excesscurrents in the range of %-200% of the nominal rating of the circuitbreaker, the bimetallic strip 20 is heated and warps so as to move theupper end thereof to the right as viewed in FIGURE 2, causing thecalibrating screw 21 to engage the thermal trip bar 27, rotating itclockwise as viewed and causing the projection 27A to engage the latchmember 25. This engagement rotates the latch member 25 also in clockwisedirection to disengage the retaining portion 25A from the trip member 17to cause tripping.

Operation of the magnetic tripping means Upon the occurrence of excesscurrents in the range of 6 to 12 times the nominal rating of the circuitbreaker, the coil 23 is energized so as to draw the armature 35 towardthe field piece 36, rotating the actuating member 28 clockwise as viewedand causing the projections 28A to engage the magnetic trip bar 2513,thereby rotating the latch member 25 in clockwise direction to releasethe latch projection 25A from the trip member 17.

Referring to FIGURE 4, a diagram is shown illustrating what is believedto be the magnetic flux flow in the invention. Assuming the currentconditions to be in a direction to cause flux in the directionillustrated through the core member 38, it will be observed that theflux divides and passes through the field piece 36 in oppositedirections and thence across the working air gaps 40 to the side wallportions of the armature 35, and thence from the central portion of thebackv wall of the armature 35 through the bimetallic strip 20 returningto the core member 38. Also, it is believed that a portion 41 of themagnetic flux which may be designated as leakage flux, flows from theside wall portions of the armature 35 edgewise through the bimetallicstrip 20 returning to the core member 38. It will be observed,nevertheless, that all of the flux, including the leakage flux 41 isrequired to pass across the working air gaps 40, thus providing a veryhighly efficient assembly, and minimizing the number of turns requiredin the coil 23.

This arrangement may be contrasted to other possible arrangements, such,for URES 5 and 6. Thus, in FIGURE 5, it will be observed that fluxflowing upwardly through the core member 38' divides and passes throughthe side wall portions of the stationary magnetic field piece 36', andthat while a portion thereof passes across the working air gaps 40', asecond portion 41 passes through the bimetallic member 20' and returnsto the core member 38' without passing across the air gaps 40'. InFIGURE 6, the bimetallic strip 20" is positioned in the spaceintermediate the stationary field piece 36" and the armature 35". Itwill be observed that in this form also, the leakage flux 41'' is freeto pass through the bimetallic strip 20 without having first bridged theworking gaps 41". In accordance with the invention, however, bypositioning the portion of the bimetallic strip which extends betweenthe magnetic members 35, 36, entirely within the space defined by theback wall and side walls of the magnetic member 35, it is assured thatvirtually all the flux which passes laterally through the bimetallicstrip will also be required to pass across the working gaps 40.

While the term field piece and armature have been used in referring tothe members 36, 35 respectively, it will be readily appreciated that themember 35 could, if desired, be made a stationary member and the member36 could be the movable member.

While the invention has been described in one particular embodiment, itwill be readily apparent that many modifications thereof can readily bemade, and it is therefore intended by the appended claims to cover allsuch example as illustrating in FIG modifications as fall within thetrue spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electric circuit breaker comprising:

(a) an insulating casing;

(b) at least two relatively movable contacts in said insulating casing;

(0) operating means in said insulating casing for moving said contactsbetween open and closed circuit positions, said operating meansincluding a releasable member releasable to cause automatic opening ofsaid contacts and a trip member movable to cause release of saidreleasable member;

(d) trip means in said insulating casing for causing tripping movementof said trip member upon the occurrence of predetermined currentconditions through said circuit breaker, said trip means includingmagnetic tripping means and thermal tripping means;

(e) said magnetic tripping means comprising a pair of magnetic memberssupported in spaced apart relation;

(f) a generally cylindrical magnetic core member having one end thereofmounted on a first one of said magnetic members and having its free endspaced from the second of said magnetic members;

(g) a winding on said core connected electrically in series with saidcontacts;

(h) an elongated bimetallic strip extending between said free end ofsaid core and said second magnetic member;

(i) said second magnetic member being generally channel-shaped andincluding a back wall and side wall portions extending therefrom;

(j) the portion of said bimetallic strip which extends between saidmagnetic members being positioned within the space defined by said backwall and said side walls of said second magnetic member.

2. An electric circuit breaker as set forth in claim 1 wherein saidcircuit breaker also includes means connecting said bimetallic stripelectrically in series with said winding.

3. An electric circuit breaker as set forth in claim 1 wherein saidportion of said bimetallic strip which extends between said magneticmembers is spaced from a line interconnecting the end portions of saidside wall portions of said second magnetic member.

4. An electric circuit breaker as set forth in claim 1 wherein saidcircuit breaker also comprises means fixedly mounting one end of saidbimetallic strip in said casing closely adjacent said magnetic tripassembly.

5. An electric circuit interrupter as set forth in claim 1 wherein saidcircuit breaker comprises a plurality of pole chambers, each of saidpole chambers containing current responsive means similar to said tripmeans for causing tripping movement of said trip member.

References Cited UNITED STATES PATENTS 2,447,652 8/1948 Jennings 335-372,842,635 7/1958 Cole 335---37 3,178,535 4/1965 Gelzheiser 335363,264,427 8/1966 Hurtle 33535 BERNARD A. GILHEANY, Primary Examiner.

HAROLD BROOME, Assistant Examiner.

